Clostridium difficile (C. difficile) is a common nosocomial pathogen and a major cause of morbidity and mortality among hospitalized patients throughout the world. Kelly et al., New Eng. J. Med., 330:257-62, 1994. The increased use of broad spectrum antibiotics and the emergence of unusually virulent strains of C. difficile have lead to the idea that vaccines may be well suited to reduce disease and death associated with this bacterium. C. difficile has few traditional antibiotic options and frequently causes a recurring disease (25% of cases). C. difficile claims about 20,000 lives in the USA alone per year and causes around 500,000 confirmed infections. Recently, more virulent strains of C. difficile have emerged that produce more toxin such as the B1/NAB1/027 strain, which also has a decreased susceptibility to metronidazole. Outbreaks of C. difficile have necessitated ward and partial hospital closure. With the increasing elderly population and the changing demographics of the population, C. difficile is set to become a major problem in the 21st century. The spectrum of C. difficile disease ranges from asymptomatic carriage to mild diarrhea to fulminant pseudomembranous colitis.
C. difficile has a dimorphic lifecycle whereby it exists both as an infectious and tough spore form and a metabolically active toxin-producing vegetative cell. C. difficile-associated disease (CDAD) is believed to be caused by the vegetative cells and more specifically the actions of two toxins, enterotoxin toxin A and cytotoxin toxin B. Vaccines and therapy for C. difficile have been to date focused upon the toxins (A and B), toxoids of A and B, recombinant fragments of A and B, and vegetative cell surface layer proteins (SLPAs).
Toxin A is a high-molecular weight protein that possesses multiple functional domains. The toxin is broken up into 4 functional domains: an amino-terminal glucosyltransferase that modifies Rho-like GTPases leading to cytoskeletal dysregulation in epithelial cells, an autocatalytic cysteine protease domain, a hydrophobic membrane-spanning sequence, and a highly repetitive carboxy-terminal host-cell binding domain. The carboxy terminal domain anchors the toxin to the host cell carbohydrate receptors on intestinal epithelial cells which initiates the internalization process thereby delivering the amino-terminal enzymatic domains to the cytoplasm of the target cells. The delivery of the enzymatic domain and glucosyltransferase activity leads to diarrhea and inflammation due to the apoptotic cell death of the intoxicated cells.
Many studies have shown the importance of antibodies against the toxins in affecting the disease outcome. Studies have also shown the correlation between serum anti-toxinA antibodies with protection from CDAD and relapse. These studies have led to the creation of toxin mAb therapies for CDAD.
Despite these advances, there is an unmet need for effective treatment and/or prevention of C. difficile associated infections including prevention from relapse of CDAD. The present invention provides mouse and humanized antibodies to toxin A to satisfy these and other needs.